The present invention relates to a device for controlling the combustion process in a combustion engine. The invention relates to such a device for reducing soot emissions but also carbon monoxide and hydrocarbon in combustion engines in which the fuel/cylinder gas mixture is ignited by compression heat generated in the cylinder. The invention also relates to a device having a high efficiency combustion.
Soot particles (or particulates) are a product which, during combustion, can both be formed and subsequently oxidized into carbon dioxide (CO2). The quantity of soot particles measured in the exhaust gases is the net difference between formed soot and oxidized soot. The process is very complicated. Combustion with fuel-rich, fuel/air mixture with poor mixing at high temperature produces high soot formation. If the formed soot particles can be brought together with oxidizing substances such as oxygen atoms (0), oxygen molecules (02), hydroxide (OH) at sufficiently high temperature for a good oxidation rate, then a greater part of the soot particles can be oxidized. In a diesel engine, the oxidation process is considered to be in the same order of magnitude as the formation, which means that net soot production is the difference between formed quantity of soot and oxidized quantity of soot. The net emission of soot can therefore be influenced firstly by reducing the formation of soot and secondly by increasing the oxidation of soot. Carbon monoxide emissions (CO) and hydrocarbon emissions (HC) are normally very low from a diesel engine. Yet the percentages can rise if unburnt fuel ends up in relatively cool regions. Such regions are, in particular, zones with intense cooling located close to the cylinder wall. Another example is cavities between piston and cylinder lining.
Nitrogen oxides (NOx) are formed from the nitrogen content in the air in a thermal process which has a strong temperature dependency and depends on the size of the heated-up volume and the duration of the process.
A combustion process in which the fuel is injected directly into the cylinder and is ignited by increased temperature and pressure in the cylinder is generally referred to as the diesel process. When the fuel is ignited in the cylinder, combustion gases present in the cylinder undergo turbulent mixing with the burning fuel, so that a mixture-controlled diffusion flame is formed. The combustion of the fuel/gas mixture in the cylinder gives rise to heat generation, which causes the gas in the cylinder to expand and which hence causes the piston to move in the cylinder. Depending on a number of parameters, such as the injection pressure of the fuel, the quantity of exhaust gases recirculated to the cylinder, the time of injection of the fuel and the turbulence prevailing in the cylinder, different efficiency and engine emission values are obtained.
Below follows an example of state of the art arrangement attempting to lower both soot and NOx-emissions by controlling the flame, and trying to brake the well known “trade off” between soot emissions and nitrogen oxide emissions, which is typical of the diesel engine, and which “trade-off” is difficult to influence. The majority of measures which reduce soot emissions increase the nitrogen oxide emissions.
WO2009/058055 discloses as combustion engine with a combustion chamber comprising a piston, an injector with plurality of orifices arranged to inject spray/flame plumes, which impinge on a piston outer bowl section during most of the injection. Between spray/flame plume impingement areas and in a plane substantially perpendicular to reciprocal piston movement are arranged a first type of protrusions protruding into the combustion chamber, having a smooth form for preserving kinetic energy in the flame and for redirecting circumferential flame progress mainly towards a center axis of the piston with minimal flame-to-flame interaction. A second type of protrusions are arranged in the impingement areas, being adapted for redirecting flame progress into a circumferential flame progress direction in a plane substantially perpendicular to said reciprocal piston movement and with minimal flame-to-piston wall interaction and minimal kinetic energy loss. It is mentioned that both said protrusion types can be adapted to swirl by having an asymmetrical form that is swept to a certain degree in the flowing direction of the swirl. This is in order to meet the spray plume affected by said swirl in the right position when it impinges said impingement area.
Due to coming future emission legislation for combustion engines there is a need to further lower the emission levels in order to meet coming demands.
It is, therefore, desirable to overcome the deficiencies of the prior art and to provide an internal combustion engine containing a combustion chamber arrangement designed to further reduce undesirable soot emissions. This is done by promoting further afteroxidation of remaining soot. The soot reduction is especially important for fuels such as for example diesel. The invention further contributes to the reduction of carbon monoxide (CO) emissions and hydrocarbon (HC) emissions. The reduction of CO and HC becomes especially important for fuels such as for example DME (dimethyl ether).
It is also desirable to increase efficiency. The design of the combustion chamber according to an aspect of the present invention results in a faster combustion.
Known effects when using, for example, an increased amount of Exhaust Gas Recirculation can at least partly be compensated for by aspects of the present invention.
According to an aspect of the invention, a piston is positioned for reciprocal movement in a combustion engine cylinder between a bottom dead center position and a top dead center position, said piston including a piston crown comprising, an upper surface facing a combustion chamber, said piston crown containing a piston bowl formed by an outwardly opening cavity, said piston bowl comprising an outwardly flared outer bowl section having a concave curvilinear shape in cross section, at least one intake port arranged to provide the combustion chamber with intake air substantially without swirl, an injector arranged to inject fuel into the combustion chamber from a position adjacent a geometrical centre of said combustion chamber and having an impingement area of a progressing flame plume in said outer bowl section, and where substantially half way between said impingement areas and in a plane substantially perpendicular to said reciprocal movement are arranged a first type of protrusions protruding into the combustion chamber and having a smooth form adapted for preserving kinetic energy in a flame plume and where each of said first type of protrusions has a shape of a longitudinal ridge that extends only in the outer bowl area, and where said first type of protrusions having a left side flank and a right side flank of said ridge when seen from said injector.
The invention is characterized in that said left side flank is formed differently compared to said right side flank in order to redirect the movement of a flame plume progressing towards said left side flank in a plane perpendicular to said reciprocal movement differently compared to corresponding flame plume progressing towards said right side flank.
According to one embodiment of the invention a top of said ridge having a form that is swept to a right or left direction, when seen from said injector and in a plane perpendicular to said reciprocal movement, and where propagation of said top follows a plane that is parallel to said reciprocal movement and where said plane coincide with a geometrical central axis of the combustion engine cylinder.
According to another embodiment of the invention an upper part of said ridge, positioned away from a bottom of said piston bowl, having a form that is swept in one first direction in a plane perpendicular to an axis of reciprocation of the piston and when seen from said injector, and a lower part of said ridge, positioned close to said bottom of said piston bowl, having a form that is swept in an opposite direction to said first direction when seen from said injector and in another plane perpendicular to said axis of reciprocation of the piston, and where a distance parallel to an axis of reciprocation of the piston and between said planes is at least half of a total length of said ridge.
In a further embodiment of the invention one of said upper or lower parts swept in said first direction having a first top of ridge section where extension of said first top of ridge section coincides with a first plane that is parallel to said reciprocal movement and where said first plane coincides with said geometrical central axis of the combustion engine cylinder, and where the other of said upper or lower parts swept in said opposite direction having a second top of ridge section where extension of said second top of ridge section coincides with a second plane that is also parallel to said reciprocal movement and where said second plane also coincides with said geometrical central axis of the combustion engine cylinder, and where a first distance between said first plane and said second plane, measured substantially at a position of said ridge or first type of protrusion, is less than a second distance corresponding to a base width of said first type of protrusions at a portion of said first type of protrusions having the biggest width.
According to another embodiment of the invention having a top of said ridge where extension of said top of said ridge coincides with a plane having an angle to a geometrical central axis of the combustion engine cylinder and where said plane coincides only in one point with said geometrical central axis of the combustion engine cylinder. In a further embodiment said angle is between 0 and 30 degrees.
In a further embodiment of the invention a second type of protrusions is arranged in the impingement area between said first type of protrusions, and where said second type of protrusions being adapted for redirecting flame progress directed towards the impingement area mainly into a circumferential flame progress direction in a plane substantially perpendicular to said reciprocal movement and with minimal flame-to-piston wall interaction and minimal kinetic energy loss.
In a further embodiment of the invention said first type of protrusions are arranged for redirecting circumferential flame progress mainly towards a center axis of the piston with minimal flame-to-flame interaction.